Effect of Al ions on fluorescence properties of YPO4: Eu phosphors

Different concentrations of Al³⁺-doped YPO₄:Eu_0.05 powder phosphors have been synthesized by the conventional solid state reaction method and are characterized by X-ray diffraction (XRD), field emission scanning electronic microscopy (FESEM), photoluminescence excitation (PLE) and emission (PL) investigations. The influence of Al³⁺-doping on crystallinity, grain size and PL intensity of the YPO₄:Eu phosphors has been investigated. These characteristics are found improved with increase in concentration of Al³⁺ ions from 0.00 to 0.10 mol and then decreased for higher concentrations. The results are discussed in comparison with earlier reported similar works.     

Luminescence investigation of Eu activated molybdates red phosphors and their applications in near-UV light-emitting diodes

The red phosphors, Na₅La_1−xSm_x(MoO₄)₄ and Na₅Eu_1−xSm_x(MoO₄)₄, were prepared by solid-state reaction technique at high temperature. Their structure and photo-luminescent properties were investigated. The excitation bands around 400 nm of these phosphors are broadened by Sm³⁺-Eu³⁺ co-doping. And the possible energy transfer process from Sm³⁺ to Eu³⁺ in these compounds is also discussed briefly. The phosphor Na₅Eu_0.90Sm_0.10(MoO₄)₄ exhibits efficient red-emitting with broadened absorption around 400 nm and appropriate CIE chromaticity coordinates (x = 0.66, y = 0.34), bright red light can be observed from the red LED based Na₅Eu_0.90Sm_0.10(MoO₄)₄.     

Luminescence properties of Nd-doped (Y,Gd)BO3 phosphors

A system of 0.03 mol Nd³⁺-doped (Y,Gd)BO₃ phosphors were prepared by the conventional solid state reaction method for different concentrations of Gd³⁺ ions and were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and NIR emission measurements. The emitted radiation was dominated by 1057 nm peak in the NIR region as a result of ⁴F_3/2 → ⁴I_11/2 transitions of Nd³⁺ ions. As the concentration of Gd³⁺ ions increases from 0.00 to 0.57 mol, the grain sizes and the intensity of NIR emission peaks were improved. The results are discussed in comparison with similar reported works.     

Luminescence properties of (Ca,Y)-α-SiAlON:Eu phosphors

(Ca,Y)-α-SiAlON:Eu phosphors for white LED lamps were prepared and their luminescence properties were investigated. A red shift of emission wavelength occurred when Ca was partially replaced by Y. Raising the sintering temperature also caused the red shift. As a result, the peak emission wavelength varied from 585 nm to 608 nm, with increasing of the Y content and the sintering temperature, and therefore the chromaticity range of (Ca,Y)-α-SiAlON phosphors extended to longer wavelength by these results. The corresponding correlated color temperature (CCT) of white LED lamps using (Ca,Y)-α-SiAlON:Eu also extended to the temperature as low as 1700 K.     

Synthesis and optical properties of green to orange tunable garnet phosphors for pcLEDs

Y_3−xLu_xAl₃MgSiO₁₂:Ce³⁺ phosphors were prepared by aqueous sol-gel technique. Samples with 0.25, 0.5, 0.75 and 1 mol-% of Ce³⁺ were fabricated and characterized by powder X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, and temperature dependent luminescence to reveal the thermal quenching. Moreover, luminous efficacies (LE), CIE 1931 color points and quantum efficiencies (QE) were calculated and discussed. XRD patterns confirmed the presence of single phase garnet for all samples independent of Ce³⁺ concentration and Y/Lu ratio. Phosphors showed broad band emission in the range 500-750 nm. The emission maximum shifts from 555 to 585 nm depending on the Ce³⁺ concentration and Y/Lu ratio. Quantum efficiency of the phosphors decreased with rising Ce³⁺ concentration and increased with increasing Lu content.     

Facile combustion synthesis and photoluminescence properties of Ce3+ doped Sr2La8(SiO4)6O2 phosphors

The Sr₂La₈(SiO₄)₆O₂:Ce³⁺ powder phosphor with apatite structure has been successfully synthesized via a facile route of sol-combustion technique. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and photoluminescence (PL) spectroscopy were used to characterize the as-prepared samples. Sr₂La₈(SiO₄)₆O₂:Ce³⁺ phosphor was composed of particles with average sizes range about 300 nm. The phosphor exhibited an absorption ranging from 220 to 390 nm in ultraviolet range and a broad blue-violet emission band peaked at 403 nm with a CIE coordinates of (0.167, 0.028). The concentration quenching mechanism was also determined to be dipole–dipole interaction.     

Persistent luminescence of SrAl2O4: Eu,Dy, Cr phosphors in the tissue transparency window

We report on the persistent luminescence of SrAl₂O₄: Eu²⁺, Cr³⁺ phosphor centered at 760 nm. The phosphor was prepared by sol-gel-combustion method. Persistent luminescence from Cr³⁺ lasted for hundreds of seconds, comparable to the long afterglow from Eu²⁺ ions in the visible region based on the continuous energy transfer from Eu²⁺ ions to Cr³⁺ ions. The introduction of Dy³⁺ ions into the phosphor further prolonged the afterglow time of Eu²⁺ and Cr³⁺ ions through the depth control of the charge traps. The optimum doping concentrations for Eu²⁺, Cr³⁺ and Dy³⁺ were 1%, 2% and 1.5%, respectively.     

Photoluminescence of CaAlSiN3:Eu2+-based fine red-emitting phosphors synthesized by carbothermal reduction and nitridation method

In this research, we have presented the synthesis and characterization of the various Ca_1−xEu_xAl_0.76Si_1.18N₃ (x = 0.01 ∼ 0.1) red-emitting phosphors, which were successfully prepared by carbothermal reduction and nitridation (CTRN) method without the strict needs of high pressure. Here, raw materials were CaCO₃, AlN, Si₃N₄, Eu₂O₃, and C. In particular, C was considered as efficient and robust reducing agent. The influences of reaction temperature, holding time, C content, and Eu²⁺ concentration were investigated in the crystal phase compositions and photoluminescence properties of the as-prepared phosphors. Importantly, CaAlSiN₃:Eu²⁺-based red phosphors with interesting properties were obtained with reaction temperature at 1600 °C for 4 h by atmospheric N₂–10%H₂ pressure, and the C/O ratio of 1.5:1, respectively. The emission peak positions of as-prepared phosphors were red-shifted from 607 nm to 654 nm with Eu²⁺ concentration from 1 mol% to 10 mol%. Meanwhile the highest luminescence intensity was achieved with 2 mol% of Eu²⁺ concentration, which showed high external quantum efficiency up to 71%. Combining the phosphor blend of green-emitting β-sialon:Eu²⁺, yellow-emitting Ca-α-sialon:Eu²⁺, and red-emitting Ca_0.98Eu_0.02Al_0.76Si_1.18N₃ with a blue LED (light emitting diodes), warm white LED can be generated, yielding the color rendering index (Ra) of 93 at correlated color temperature (CCT) of 3295 K. These results indicate that CaAlSiN₃:Eu²⁺-based red-emitting phosphors prepared by facile CTRN are highly promising candidates for warm white LEDs.     

Preparation,characterization, and photoluminescence study of PVA/ZnO nanocomposite films

ZnO nanoparticles with average diameter of 25 nm were synthesized by a modified sol–gel method and used in the preparation of (in wt.%) (100 − x) poly(vinyl alcohol) (PVA)/x ZnO nanocomposite films, with x = 0, 1, 2, 3, 4, and 5. The PVA/ZnO films were exposed to UV radiation for 96 h and their thermal, morphological, and spectroscopic properties were investigated. In inert atmosphere, the nanocomposite films showed lower thermal stability than the pure PVA film, and the calorimetric data suggest an interaction between PVA and ZnO in the nanocomposite films. Some crystalline phases could be seen in the films with ZnO, and a direct dependence on the ZnO concentration was also observed. The original structure of ZnO nanoparticles remained unaltered in the PVA matrix and they were uniformly distributed on the film surface. The roughness of the PVA film was not modified by the addition of ZnO; however, it increased after 96 h of UV irradiation, more significantly in the nanocomposite films. The films showed an absorption band centered at 370 nm and a broad emission band in the UV–vis region when excited at 325 nm.     

掺杂稀土的xSrO.yA12O3系长余辉发光材料的制备及其光学性能

利用SrCO3-A12O3-RE(NO3)3(REEu,Dy)粉体为原料,加入少量酒精,进行预混合、球磨、干燥.将此混合粉体在还原气氛下高温烧成,最终制得不同发光性能的xSrO.yAl2O3RE(REEu,Dy)光致发光材料,并对其性能进行了研究.发光粉体的发射光谱表明,随着A12O3/SrO(摩尔比x)的增加,其相应粉体发射光谱的主峰位置(λE)逐渐向短波方向移动,符合λE=531.018-23.028X关系式.余辉衰减曲线表明,这些发光材料均具有一定的长余辉特性.从而说明只要控制一定的Al2O3/SrO比例,即可获得发光颜色为紫色到绿色的多种发光材料.对于其长余辉机制,认为是加入的Dy3+起到了陷阱能级的作用,它将部分空穴俘获,并在热扰动下,慢慢将空穴释放出来,并再次与介稳态Eu1+复合发光,从而达到延长余辉的作用.     

Monodisperse colloidal spheres for (Y,Eu)2O3 red-emitting phosphors: establishment of processing window and size-dependent luminescence behavior

Abstract

The urea-based homogeneous precipitation method was introduced in the preparation of monodisperse colloidal spheres for (Y_0.95Eu_0.05)₂O₃ red-emitting phosphors, and the processing window was defined. Particle size and shape are significantly affected by the ion concentration and the urea/RE³⁺ molar ratio R (RE³⁺=Y³⁺+Eu³⁺). A low ion concentration is beneficial in forming monodisperse spheres and extending their formation domain. Increasing R results in a gradual change in the composition of spherical particles from the core-shell Eu(OH)CO₃@Y(OH)CO₃ structure to a homogeneous solid solution, thereby significantly lowering the calcination temperature at which precursors convert to oxides. Upon UV excitation into the charge-transfer band at 254 nm, the uniform phosphor spheres of (Y_0.95Eu_0.05)₂O₃ exhibit typical red emissions at 613 nm; the emission is stronger from larger particles mainly because of their smaller surface area. Both the luminescence intensity and quantum efficiency of the oxide phosphors increase with elevated calcination temperatures. The spherical shape and excellent dispersion of the precursor particles (～450 nm in diameter) have been well retained after calcination at 1000 ^○C for 4 h, and the resultant oxide phosphors exhibit external and internal quantum efficiencies of 50 and 82%, respectively.     

Improving crystalline morphology and photoluminescent properties of BaY2ZnO5:Eu phosphors prepared using microwave assisted sintering

This paper describes an investigation of the crystalline morphology and photoluminescent properties of BaY₂ZnO₅:Eu³⁺ powders using microwave assisted sintering. For comparison, the properties of BaY₂ZnO₅:Eu³⁺ powders prepared by a solid-state reaction in a conventional furnace were also investigated. The results showed that the formation time of the single phase for BaY_1.8Eu_0.2ZnO₅ powders sintered at 1250 °C in the microwave furnace is significantly reduced to 1 h, and the emission spectra of BaY_1.8Eu_0.2ZnO₅ powders excited at 395 nm exhibit a maximum peak assigned to ⁵D₀ → ⁷F₂ transition. In addition, the emission intensity of the prepared powder is definitely enhanced, compared to that sintered at 1250 °C/10 h in a conventional sintering furnace.     

红色荧光粉Ca_9Al(Po_4)_7:Eu~(3+)的制备与发光特性

本文采用高温固相法合成了Ca9Al(Po4)7:Eu3+红色荧光粉,并对其发光特性进行了研究。该荧光粉在350nm-410nm有一个宽带激发峰,适用于UVLED管芯的激发;在紫外激发下的发射峰由位于589nm和593nm,612nm、616nm和619nm,654nm及688nm四组线状峰构成,分别对应于Eu3+的(5D0～7F1)、(5D0～7F2)、(5D0～7F3)及(5D0～7F4)特征跃迁,呈现红色发光。探讨了掺杂的Eu3+浓度对样品发光强度的影响,其最佳掺杂浓度为5%。研究了其自身浓度猝灭机理,为电偶极-电四极相互作用。发现不同电荷补偿剂Li+,Na+,K+的引入均能使发光强度得到提高,尤其以Li+最佳,发光强度提高了大约35%。结果表明,Ca9Al(Po4)7:Eu3+是一种适用于UVLED管芯激发的用于白光LED的红色荧光粉。     

Precipitation based synthesis and luminescence of Ln (Eu,Ce, Dy,Sm, Tb) activated BaCa2Si3O9-Walstromite cyclosilicate phosphors

A series of new phosphors of BaCa₂Si₃O₉:Ln³⁺, (Ln = Eu, Ce, Dy, Sm, Tb) were synthesized by precipitation based method. Good crystallinity was achieved after annealing the sample at 750 °C for 1 h in air. X-ray powder diffraction (XRD) result confirmed the formation of desired BaCa₂Si₃O₉ host. The photoluminescent excitation and emission properties of Ln³⁺, (Ln = Eu, Ce, Dy, Sm, Tb) activated BaCa₂Si₃O₉ were investigated in detail. The photoluminescence (PL) analysis of individual Ln³⁺, (Ln = Eu, Ce, Dy, Sm, Tb) activated BaCa₂Si₃O₉ phosphors exhibits interesting characteristic emission properties in their respective regions. From the measured emission spectra, Judd–Ofelt (J–O) intensity parameters (Ω₂, Ω₄, Ω₆) have been calculated and using these J–O parameters various radiative parameters such as radiative transition probabilities (A_rad), radiative lifetimes (τ_R), branching ratios (β_R) and relative quantum yield have been calculated for the studied ions.     

Chemical and photoluminescence analyses of new carbon-based boron oxynitride phosphors

Analyses of newly developed carbon-based boron oxynitride phosphors using an electron energy-loss spectrometer and a spectroflurophotometer were carried out. The results showed that the prepared phosphor powder has covalently bonded boron, nitrogen, and oxygen atoms with a soft carbon framework. Photoluminescence characterization revealed that the resultant phosphor has a direct bandgap transition with defect broadened band edges, resulting in a high quantum efficiency, because the atomic distances of the phosphor are smaller than those of conventional carbon-based boron nitride compounds, which have an indirect bandgap transition and a low quantum efficiency. The atomic distances of the phosphor are smaller owing to the presence of oxygen atoms, which have a higher electron affinity and a smaller covalent bond radius compared with boron, carbon and nitrogen.     

Tunable color emitting of CaAl2Si2O8: Eu,Tb phosphors for light emitting diodes based on energy transfer

A series of single-phased CaAl₂Si₂O₈: Eu, Tb phosphors have been synthesized at 1400 °C via a solid state reaction. The emission bands of Eu²⁺ and Eu³⁺ were observed in the air-sintered CaAl₂Si₂O₈: Eu phosphor due to the self-reduction effect. Tb³⁺ ions that typically generated green emission were added in CaAl₂Si₂O₈: Eu phosphor for contributing for a wider-range tunable emission. Energy transfer from Eu²⁺ to Tb³⁺ and the modulation of valence distribution of Eu²⁺/Eu³⁺ that contributes to the tunable color emitting were elucidated. More importantly, a white emission can be obtained by controlling the codoped contents of Li⁺ as well as suppressing the self-reduction degree of Eu. The white light emitting with the color coordinate (0.326, 0.261) was obtained, which indicates that CaAl₂Si₂O₈: Eu, Tb is a promising tunable color phosphor for application in ultraviolet light emitting diodes (UV-LEDs).     

Preparation and characterization of sol-gel Li and Al codoped ZnO thin films

Li and Al codoped ZnO (LAZO) thin films have been prepared by a sol-gel method and their structural and optical properties have been investigated. The prepared LAZO films had an average transmittance of over 85% in the visible range. The UV absorption edge was red-shifted with Li-doping, whereas it was blue-shifted with Al-doping. A broad yellowish-white emission was observed from the LAZO films annealed above 600 °C. The visible emission was enhanced with increasing annealing temperature and dopant concentration.     

Preparation and characterization of Sr4Al2O7:Eu, Eu phosphors

A new composition of red strontium aluminate phosphor (Sr₄Al₂O₇:Eu³⁺, Eu²⁺) is synthesized using a solid state reaction method in air and in a reducing atmosphere. The investigation of firing temperature indicates that a single phase of Sr₄Al₂O₇ is formed when the firing temperature is higher than 1300 °C and that a Sr₃Al₂O₆ phase is formed as the main peak below 1300 °C. The effects of firing temperature and doping concentration on luminescent properties are investigated. Sr₄Al₂O₇ phosphors exhibit the typical red luminescent properties of Eu³⁺ and Eu²⁺. A comparison photoluminescence study with Sr₃Al₂O₆ phosphor shows that Sr₄Al₂O₇ has higher emission intensity than Sr₃Al₂O₆ as a result of the higher optimum doping concentration of Sr₄Al₂O₇ phosphor.     

Porous MAl2O4:Eu (Eu), Dy (M = Sr, Ca, Ba) phosphors prepared by Pechini-type sol-gel method: The effect of solvents

In this work, a series of porous Eu²⁺-doped alkaline earth aluminates phosphors including MAl₂O₄:Eu²⁺ (Eu³⁺), Dy³⁺ (M = Sr, Ca, Ba) have been prepared by Pechini-type sol-gel approach, using citric acid as chelating ligand and ethylene glycol (or H₂O) as solvent. The as-obtained samples were characterized by means of XRPD, FESEM and PL techniques. MAl₂O₄:Eu²⁺, Dy³⁺ (M = Sr, Ca, Ba) phosphors were prepared in a reducing atmosphere (H₂/Ar, 20 + 80%) while MAl₂O₄:Eu³⁺, Dy³⁺ (M = Sr, Ca, Ba) phosphors were obtained in air. Upon changing the molar ratio of citric acid to total metal cations concentration in ethylene glycol can produce spherical phosphors and the higher molar ratio favors the formation of spherical ones. Otherwise, irregular shaped phosphors occur when conducting the reaction in pure H₂O. The irregular shaped phosphors have higher emission intensity than those spherical ones observed with the help of excitation spectra, emission spectra and decay curves.     

Luminescence concentration quenching and site-occupancy of Eu2+ ions in Na2Ca2Si3O9 phosphors derived from 45S5 glass-ceramics

The phosphors of Na₂Ca_2-2xEu_2xSi₃O₉ (x = 0, 0.03, 0.05, 0.07, 0.09) were first synthesized by sol-gel method. The crystal phase formations of the phosphors were detected by X-ray powder diffraction (XRD) measurements and the structure refinement. The photoluminescence spectra, the concentration quenching, the luminescence decay curves and the luminescence color chromaticity were measured, respectively. The excitation spectra indicate that the phosphors can be effectively excited by near UV-LED chips. Two kinds of Eu²⁺ sites centered at 545 nm and 505 nm were discussed by analyzing the spectra, concentration-dependent luminescence intensity and lifetimes. This is a potential tool for monitoring the bioactivity of 45S5 glass-ceramics in situ.